For a triangle  2D element consisting of 3 nodes a the Aspect  Ratio is calculated as the ratio of the length, h2, of the edge  of this triangle, to the height, h1. The ratio of h2 to h1 is then multiplied  by 3(1/2) /2, so that  a Â“perfectÂ” element in the shape of an equilateral triangle will be equal  to 1. This procedure is repeated for the remaining two edges of the triangle,  and the largest value is retained as the Aspect  Ratio for the element.
+ + + + + +
where :
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+
+ 
For a quadrangle 2D element consisting of 4 nodes the  Aspect Ratio is the ratio of the  element's longest side to its shortest side.
To apply the Aspect Ratio quality criterion to your mesh:
 1.9.1